It has been appreciated that if a motor vehicle, such as a motor car, is involved in a rear-end collision--that is to say if a following vehicle runs into the back of the car--the occupants of the struck car often suffer from neck injuries.
It is to be understood that during a rear-end collision of this type, the vehicle that is struck is subjected to a forward acceleration. This imparts a forward acceleration to the seats of the vehicle. The squab and the back of each occupied seat engage the posterior and torso of the occupant of the seat and impart a substantial acceleration to the posterior and torso of the occupant. However, no corresponding acceleration is immediately imparted to the head of the occupant. The head is a part of the body that has substantial mass, and consequently the head has substantial inertia.
Thus, whilst the posterior and torso of the occupant of the vehicle are accelerated forwardly as a result of the rear-end collision, the head of the occupant of the vehicle initially remains stationary. This causes the neck initially to adopt a "S"-shaped configuration as the lower part of the neck moves forwardly, whilst remaining vertical, and the upper part of the neck remains in its initial position. Subsequently, the head begins to rotate, and the neck then occupies a curved configuration. The head subsequently moves forwardly. Research has shown that "whiplash" injuries may occur when the neck adopts the "S"-shaped configuration, if the head is moving, relative to the torso, at a substantial speed.